In the prior art various updraft combustion devices for heating water have been known, such as the common gas fueled or oil fueled household water heater with a vertical flue within a water containing casing.
However, a large part of the heat of combustion when exchanging heat to water in such devices goes up the chimney, either straight up or essentially all the way in an upward direction inside the upwardly directed flue.
To reduce such losses it has been necessary to provide taller water heating apparatus, increasing the area to be insulated and increasing the space required for installation of the water heating apparatus.